I have just seen another Black-throated Tit 2018 photograph, on the back page of Bulletin 250, taken at Ho Man Tin on 20 March 2018 by Peter Ho.

Although not a common species and only seen in a few locations, this species is probably resident in Hong Kong although it may be declining.
The following graph shows the highest count of birds and number of locations where they were recorded since 1990.

Birds were presumably present in Hong Kong in 2017 (also 2000 and 2001) but not reported.
If anyone has a photograph of a Black-throated Tit taken in Hong Kong in 2017, please post here with date and location. Otherwise this will be a missing species in the 2017 HK Bird Report.